appender: replace chrono with time (#1652)

## Motivation

This PR continues the work started in
#1646 to replace `chrono` with
`time`. I'll refer to @hawkw's motivation:

> Currently, `tracing-subscriber` supports the `chrono` crate for
> timestamp formatting, via a default-on feature flag. When this code
> was initially added to `tracing-subscriber`, the `time` crate did not
> have support for the timestamp formatting options we needed.
>
> Unfortunately, the `chrono` crate's maintenance status is now in
> question (see #1598). Furthermore, `chrono` depends on version 0.1 of
> the `time` crate, which contains a security vulnerability
> (https://rustsec.org/advisories/RUSTSEC-2020-0071.html). This
> vulnerability is fixed in more recent releases of `time`, but `chrono`
> still uses v0.1.

## Solution

I've replaced chrono with time 0.3. Unfortunately, some of chrono's
builders for DateTimes are not present in `time`, which required the
usage of `macro_rules!` macros to construct some of the hard-coded
times. I also took the opportunity to tidy some of the tests and change
the internal representation of `Rotation::NEVER` from year 9,999 to an
`Option::None`.

This branch changes `tracing-appender`'s MSRV from Rust 1.42 to Rust
1.51, the MSRV for the `time` crate when certain required feature flags
are enabled. This does *not* effect the MSRV for other crates in this
repository.

.github/workflows/CI.yml

@@ -42,7 +42,24 @@ jobs:
       uses: actions-rs/cargo@v1
       with:
         command: check
-        args: --all
+        args: --all --exclude=tracing-appender
+
+  # TODO: remove this once tracing's MSRV is bumped.
+  check-msrv-appender:
+    # Run `cargo check` on our minimum supported Rust version (1.51.0).
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@main
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: 1.51.0
+        profile: minimal
+        override: true
+    - name: Check
+      uses: actions-rs/cargo@v1
+      with:
+        command: check
+        args: --lib=tracing-appender
 
   check:
     # Run `cargo check` first to ensure that the pushed code at least compiles.

tracing-appender/Cargo.toml

@@ -21,14 +21,15 @@ edition = "2018"
 
 [dependencies]
 crossbeam-channel = "0.5.0"
-chrono = { version = "0.4.16", default-features = false, features = ["clock", "std"] }
+time = { version = "0.3", default-features = false, features = ["formatting"] }
 
 [dependencies.tracing-subscriber]
 path = "../tracing-subscriber"
 version = "0.2.7"
 default-features = false
-features = ["fmt"]
+features = ["fmt", "std"]
 
 [dev-dependencies]
 tracing = { path = "../tracing", version = "0.1" }
+time = { version = "0.3", default-features = false, features = ["formatting", "parsing"] }
 tempfile = "3"

tracing-appender/README.md

@@ -36,7 +36,7 @@ allows events and spans to be recorded in a non-blocking manner through a
 dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] 
 that can be used with _or_ without the non-blocking writer.
 
-*Compiler support: [requires `rustc` 1.42+][msrv]*
+*Compiler support: [requires `rustc` 1.51+][msrv]*
 
 [msrv]: #supported-rust-versions
 
@@ -145,17 +145,17 @@ fn main() {
 
 ## Supported Rust Versions
 
-Tracing is built against the latest stable release. The minimum supported
-version is 1.42. The current Tracing version is not guaranteed to build on Rust
-versions earlier than the minimum supported version.
+`tracing-appender` is built against the latest stable release. The minimum supported
+version is 1.51. The current `tracing-appender` version is not guaranteed to build on
+Rust versions earlier than the minimum supported version.
 
 Tracing follows the same compiler support policies as the rest of the Tokio
 project. The current stable Rust compiler and the three most recent minor
-versions before it will always be supported. For example, if the current stable
-compiler version is 1.45, the minimum supported version will not be increased
-past 1.42, three minor versions prior. Increasing the minimum supported compiler
-version is not considered a semver breaking change as long as doing so complies
-with this policy.
+versions before it will always be supported. For example, if the current
+stable compiler version is 1.45, the minimum supported version will not be
+increased past 1.42, three minor versions prior. Increasing the minimum
+supported compiler version is not considered a semver breaking change as
+long as doing so complies with this policy.
 
 ## License
 

tracing-appender/src/inner.rs

@@ -2,23 +2,23 @@ use std::io::{BufWriter, Write};
 use std::{fs, io};
 
 use crate::rolling::Rotation;
-use chrono::prelude::*;
 use std::fmt::Debug;
 use std::fs::{File, OpenOptions};
 use std::path::Path;
+use time::OffsetDateTime;
 
 #[derive(Debug)]
 pub(crate) struct InnerAppender {
     log_directory: String,
     log_filename_prefix: String,
     writer: BufWriter<File>,
-    next_date: DateTime<Utc>,
+    next_date: Option<OffsetDateTime>,
     rotation: Rotation,
 }
 
 impl io::Write for InnerAppender {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        let now = Utc::now();
+        let now = OffsetDateTime::now_utc();
         self.write_timestamped(buf, now)
     }
 
@@ -32,7 +32,7 @@ impl InnerAppender {
         log_directory: &Path,
         log_filename_prefix: &Path,
         rotation: Rotation,
-        now: DateTime<Utc>,
+        now: OffsetDateTime,
     ) -> io::Result<Self> {
         let log_directory = log_directory.to_str().unwrap();
         let log_filename_prefix = log_filename_prefix.to_str().unwrap();
@@ -49,15 +49,15 @@ impl InnerAppender {
         })
     }
 
-    fn write_timestamped(&mut self, buf: &[u8], date: DateTime<Utc>) -> io::Result<usize> {
+    fn write_timestamped(&mut self, buf: &[u8], date: OffsetDateTime) -> io::Result<usize> {
         // Even if refresh_writer fails, we still have the original writer. Ignore errors
         // and proceed with the write.
         let buf_len = buf.len();
         self.refresh_writer(date);
         self.writer.write_all(buf).map(|_| buf_len)
     }
 
-    fn refresh_writer(&mut self, now: DateTime<Utc>) {
+    fn refresh_writer(&mut self, now: OffsetDateTime) {
         if self.should_rollover(now) {
             let filename = self.rotation.join_date(&self.log_filename_prefix, &now);
 
@@ -75,8 +75,12 @@ impl InnerAppender {
         }
     }
 
-    fn should_rollover(&self, date: DateTime<Utc>) -> bool {
-        date >= self.next_date
+    fn should_rollover(&self, date: OffsetDateTime) -> bool {
+        // the `None` case means that the `InnerAppender` *never* rorates log files.
+        match self.next_date {
+            None => false,
+            Some(next_date) => date >= next_date,
+        }
     }
 }
 

tracing-appender/src/lib.rs

@@ -7,7 +7,7 @@
 //! a dedicated logging thread. It also provides a [`RollingFileAppender`][file_appender] that can
 //! be used with _or_ without the non-blocking writer.
 //!
-//! *Compiler support: [requires `rustc` 1.42+][msrv]*
+//! *Compiler support: [requires `rustc` 1.51+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //! [file_appender]: ./rolling/struct.RollingFileAppender.html
@@ -110,8 +110,8 @@
 //!
 //! ## Supported Rust Versions
 //!
-//! Tracing is built against the latest stable release. The minimum supported
-//! version is 1.42. The current Tracing version is not guaranteed to build on
+//! `tracing-appender` is built against the latest stable release. The minimum supported
+//! version is 1.51. The current `tracing-appender` version is not guaranteed to build on
 //! Rust versions earlier than the minimum supported version.
 //!
 //! Tracing follows the same compiler support policies as the rest of the Tokio